////////////////////////////////////////////////////////////////////////
//
// Copyright (C) 2008-2021 The Octave Project Developers
//
// See the file COPYRIGHT.md in the top-level directory of this
// distribution or <https://octave.org/copyright/>.
//
// This file is part of Octave.
//
// Octave is free software: you can redistribute it and/or modify it
// under the terms of the GNU General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// Octave is distributed in the hope that it will be useful, but
// WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License for more details.
//
// You should have received a copy of the GNU General Public License
// along with Octave; see the file COPYING.  If not, see
// <https://www.gnu.org/licenses/>.
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////////////////////////////////////////////////////////////////////////

#if ! defined (octave_ov_null_mat_h)
#define octave_ov_null_mat_h 1

#include "octave-config.h"

#include "ov.h"
#include "ov-re-mat.h"
#include "ov-str-mat.h"

// Design rationale:
// The constructors are hidden.  There is only one null matrix (or null string)
// object, that can have shallow copies.  Cloning the object returns just a
// normal empty matrix, so all the shallow copies are, in fact, read-only.
// This conveniently ensures that any attempt to fiddle with the null matrix
// destroys its special status.

// The special [] value.

class
OCTINTERP_API
octave_null_matrix : public octave_matrix
{
  octave_null_matrix (void) : octave_matrix () { }

public:

  static const octave_value instance;

  bool isnull (void) const { return true; }

  type_conv_info numeric_conversion_function (void) const;

private:

  DECLARE_OV_TYPEID_FUNCTIONS_AND_DATA
};

// The special "" value

class
OCTINTERP_API
octave_null_str : public octave_char_matrix_str
{
  octave_null_str (void) : octave_char_matrix_str () { }

public:

  static const octave_value instance;

  bool is_storable (void) const { return false; }

  bool isnull (void) const { return true; }

  type_conv_info numeric_conversion_function (void) const;

private:

  DECLARE_OV_TYPEID_FUNCTIONS_AND_DATA
};

// The special '' value

class
OCTINTERP_API
octave_null_sq_str : public octave_char_matrix_sq_str
{
  octave_null_sq_str (void) : octave_char_matrix_sq_str () { }

public:

  static const octave_value instance;

  bool is_storable (void) const { return false; }

  bool isnull (void) const { return true; }

  type_conv_info numeric_conversion_function (void) const;

private:

  DECLARE_OV_TYPEID_FUNCTIONS_AND_DATA
};

#endif
